On the importance of the location of PCMs in building walls for enhanced thermal performance

Abstract

Phase change materials (PCMs) are used to enhance the thermal storage capacity of building walls. PCM incorporation into building walls poses several design challenges; a critical one being the integration method (e.g., micro- vs. macro-encapsulation) as well as the location of PCMs within the volume of the walls. Such location is critical for wall performance in terms of controlling heat transfer rates for purposes of energy conservation and peak load shifting. This paper highlights the dependence of wall thermal performance on PCM location leading to the most optimal PCM location for the system under study. In this study, PCMs were incorporated in walls via “thermal shields” where the PCM material was encapsulated in polyethylene flat bubbles “sandwiched” between two layers of protective aluminum foil. This system is herein referred to as “PCM thermal shield (PCMTS)”. The thermal performance of the walls with and without PCMTS was evaluated experimentally using a dynamic wall simulator. PCM thermal shields (PCMTSs) were placed within the wall insulation at varying distances from the internal surface of the bounding wallboard, which happened to be the bounding layer furthest from the heating sources of the simulator. For the system under study, the results showed that the optimal location for a PCMTS was at a distance of 1/5L from the internal surface of the bounding wallboard, where L was the thickness of the insulation cavity. At this location, the average peak heat flux reduction and load shifting time were approximately 41% and 2h, respectively, when compared to the peak heat fluxes across walls without PCMTS.